A first conventional optical element with light-splitting function is disclosed in U.S. Pat. No. 9,541,720, and a second conventional optical element with light-splitting function is disclosed in U.S. Pat. No. 9,588,308. The first and second conventional optical elements change an inclination angle of a light-splitting surface to increase the distance between a light source and a photo detector. However, when the distance between the light source and the photo detector is larger than a certain value, it may cause the following disadvantages:
1. The condensation of inclined light beams is low, so that the condensing area of the light beams is larger than the light-receiving area of the photo detector, thereby resulting in reduction of the light energy received by the photo detector. To solve this disadvantage, a larger photo sensor of the photo detector may be used, which may increase the manufacturing cost.
2. The light penetration rate of each light beam from a lens to air is decreased, so that the light coupling efficiency of the light beam into an optical fiber is low. When the inclination angle of the light-splitting surface is larger than the critical angle of total reflection, the light beam is totally reflected by the light-splitting surface, and the photo detector cannot fully receive any light signal.
Therefore, how to increase the distance between the light source and the photo detector without changing the inclination angle of the light-splitting surface becomes an important issue.
A third conventional optical element disclosed in U.S. Pat. No. 6,888,9888 also includes a photo-detecting structure. However, two photo detectors of the third conventional optical element are disposed between a light source and a receiving end of an optical fiber, such that the distance between the light source and the receiving end of the optical fiber is long. A light beam emitted from the light source needs to be reflected by a reflection surface to the receiving end. Since a receiving distance deviation of the receiving end caused by an inclination angle deviation of the reflection surface is proportional to the distance between the light source and the receiving end, the inclination angle deviation of the reflection surface may cause serious receiving distance deviation. The diameter of a receiving end of a conventional optical fiber is only 50-62 micro-millimeters, and when the light beam deviates from the receiving end of the conventional optical fiber, the receiving end of the conventional optical fiber may receive low optical signal or may not receive optical signal, and thereby leading to a failed communication.